Gas composition revision



Jan. 17, 1950 E. v. HARLOW GAS COMPOSITION REVISION Filed Nov. 14, 1946 HEATING STEAM MESURING COLUMN CONDENSER AND COOLER METER NO IN 2 Em RM E o wwn mw mm N CA N z 2'2 ECEIVER HEATER m w u w s A G Snventor 684. V Hague Clflor neg Patented Jan. 17, 1950 GAS COMPOSITION REVISION Earl V. Harlow, Beaver, Pa.., assignor to Koppers Company, Inc., Pittsburgh, Pa., a corporation of Delaware Application November 14, 1946, Serial No. 709,873

11 Claims. (Cl. 48-197) ims invention relates to changing the composition of fuel gas by diffusion. More particularly the invention relates to revising the composition of coke oven gas by diffusion in which a combination of producer gas and steam is used as a sweep gas.

In a copending application of Gilbert V. Mc- Gurl, Serial No. 710,327, a method of revising the composition of coke oven gas by diffusion has been described in which producer gas is used as a sweep gas. This revising operation is carried out particularly for the purpose of adjusting the specific gravity and B. t. u. heating value to adapt the coke oven gas for use in domestic "heating appliances.

The use of producer. gas for revising coke oven gas is very desirable because the transfer of hydrogen from the coke oven gas to the producer gas acts to increase both the gravity and B. t. u. value of the coke oven gas. At the same time the B. t. 11. value of the producer gas is increased. The diffusion treatment permits a transfer of constituents between the coke oven gas and the producer gas that will provide a wide variation in the composition of both of the gases. For example, a coke oven gas can be revised to have aheating value of 530 B. t. u.s per cubic foot and a gravity of 0.55 to 0.7. The producer gas will have its heating value raised from 135 to as much as 175 B. t. u.s per cubic foot and the molecular volumes of hydrogen and carbon monoxide in the gas may be rearranged to have a ratio of 1:1 to 2:1. A gas having such a content of hydrogen and carbon monoxide is well adapted as e. synthesis gas for thehydrogenation of carbon monoxide by the Fischer-Tropsch process.

Typical analyses of a coke oven gas and producer gas are shown in the following table:

It will be seen from the table that producer gas is a heavy gas, i. e. higher molecular weight 2 than coke oven gas, so that its rate of diflusion through a porous boundary is not as rapid as the diffusion rate of hydrogen and some of the lighter hydrocarbons in the coke oven gas. I have found that if steam is used with the producer gas, as a sweep gas, the control of transfer of constituents between the gases on the opposite sides of the porous boundary may be greatly increased. Further the composition of the revised gases on opposite sides of the boundary may be much more widely varied than when producer gas is used alone as a sweep gas. Also the steam may be readily condensed and separated from the gases so that this provides another means of varying the composition of the gas being treated because the volume of steam as a dry vapor will function as a gas in difiusing through the boundary in the sameway that the producer gas difiuses through the boundary and thus when the steam is extracted from the revised gas the chemical composition will be varied.

Testshave shown that the above-mentioned coke oven gas having a specific gravity of 0.4 may be revised by the method of the present invention to raise the specific gravity from 37.5% to to have a specific gravity from 0.55to 0.7 as mentioned above.

The primary object of the present invention is to provide a method of changing the composition of coke oven gas by difiusion in which a combination of a high gravity gas with a condensible vapor may be used as a sweep gas.

Another object of the invention is to provide a method of revising coke oven gas by diffusion in which steam with a high gravity gas such as producer gas or blast furnace gas may be used as a sweep gas.

A further object of the invention is to provide a method of revising coke oven gas by diffusion in which a high molecular'weight gas is used in combination with a low molecular weight vapor as a sweep gas.

With these and other objects in view the invention consists in the method of revising coke oven gas by diffusion in which steam is used with a high specific gravity gas as a sweep gas.

The various features of the invention are illustrated in the accompanying drawing which is a diagrammatic illustration of an apparatus in which the preferred form of the diffusion method may be carried out.

amass It into a meter M. The metered gas passes through heater it into a chamber I! at the.

bottom or a diffusion apparatus. The coke oven gas then passes upwardly through a series oi tubes which have cylindrical continuations 22 that are porous boundaries through which constituents of the gas may difluse. From the porous boundary tubes 22 the gas flows through tubes 24 into an outlet chamber 28.

Producer gas for the diiiusion operation is introduced into the system through a line 28 and flows through a flow regulating valve 30. The valve 30 is used for carefully adjusting the flow volume of the producer gas so that the desired volume of sweep gas will be provided for the diffusion revising of the coke oven gas. Steam for mixture with the producer gas is introduced through a line 32 and flow regulating valve 34 to mix with the producer gas and the mixture then flows through a meter 36. The metered mixture of steam and producer gas then flows through a heater 38 where it is heated to a temperature 10 C. above the dew point oi the mixture, and then flows through a line 40 to a line 42 and enters a distributing chamber 44. The mixture of steam and producer gas acts as a sweep gas for controlling the diffusion operation. The gas is distributed into a series of tubes 46 and passes downwardly through the tubes around the diffusion boundaries 22 which are located within the tubes 46. The mixture of steam and producer gas passes in a parallel stream to the coke oven gas with countercurrent flow. After passing through the tubes 46 the revised producer gas enters a chamber 40 and then flows through a valved line 50 into a line 52. From the line 52 the mixture of revised producer gas and steam flows through a cooler through a line to a meter 62. By this means the volume of revised producer gas is measured and the volume of water or condensed steam is measured.

The revised coke oven gas leaves the chamber 20 through a line 04 and passes through a condenser, cooler and temperature conditioner 68 into a measuring column 00. The condensed steam then flows through a line 10 and the gas through a line 02 into a receiver II which acts as a separater.l The water flows out through a line 14 and the revised coke oven gas passes through a line 16 and then through a meter 18. By this means thevoiume oi the revised coke oven gas is measured and the volume or water separated is measured.

The temperature in the diflusion apparatus is maintained as nearly uniform as possible throughout the diiiusion zone. This temperatureis approximately 115 to 120 C. for coke oven gas but will be about 10 above the dew point of the gas and steam mixture, and is controlled by means of steam which is introduced through a line Ill intoa chamber 02 of the diffusion apparatus that surrounds the tubes 45. Condensate steam may leave the chamber 82 through an outlet pipe 8|. Both the coke oven gas being fed to the diflusion apparatus and the sweep gas are heated to a temperature at least 10 above the dew point of the gas and steam mixture in the heaters l6 and 38 respectively to prepare them for the diifusion operation. The temperature must be above the dew point or the gases being treated in the apparatus 4 so that no liquid is present in the boundary tubes 22.

The now regulator it controls the volume of coke oven gas which is the feed gas to the diflu- 5 sion apparatus to be revised. The flow regulating valves 30 and SI control the volumes oi producer gas and steam respectively. which acts as a sweep gas in the diffusion operation. The pressures of the feed and sweep gas on the opposite sides oi the porous diaphragm or boundary tubes 22 are very important in controlling the diffusion of the gases through the boundaries from one stream to the other. The pressure of the coke oven gas inside oi the boundary tubes is controlled by a pressure regulating valve 88 and the pressure oi the sweep gas on the outside of the boundary tubes is controlled by a pressure regulating valve ll. These valves are carefully regulated to maintain the pressure distribution for the diflusion operation. The pressure distribution of the feed and sweep gases involves several factors:

First, the pressure of the sweep gas is sumciently higher than the pressure of the feed gas so that there is a hydrodynamic flow of sweep gas through the pores oi the boundary. This hydrodynamic flow is the flow of sweep gas through the boundary pores which is not due to diflfusion but is due to the pressure diii'erential across the boundary.

Second, the size of the pores which determine the porosity of the boundary or diaphragm should be many times larger than the mean free path of the molecules of the reed gas. The mean free path of the molecules is the average distance which a molecule travels before colliding with an adjacent molecule. Depending upon the length and the resistance to flow of the pore, the average length and width or diameter of the pore may be from 1 to 10,000 times the mean free path of the molecule.

Third, the pressure of the gas streams at opposite sides of the boundary or the average pressure differential across the pores oi the boundary.

Fourth, the area of the boundary. This area 45 takes into consideration the pressure diflerentials at the inlet and outlet ends of the boundary or the average pressure diflerential over the area of the boundary. when the feed and sweep gas streams flow concurrently or in the same direction. the pressure diilerential at the entrance end is dependent upon the difference in pressure of the two gas streams. With such a flow there will be a gradual lowering of the pressure dinerential as the two streams advance across the boundary area. If the feed and sweep gas streams flow countercurrently along the boundary, then the pressure differential across the boundary at the entrance end of the sweep gas is at its maximum because the resistance of flow 60 and the diffusion of the feed gas through the boundary has lowered its pressure and the pressure of the sweep gas is at its maximum. Accordingly with countercurrent flow the diiiusion rate will be lowest at the entrance end of the 06 sweep gas and highest at the exit end of the sweep gas from the boundary area.

When carrying out the diflusion operation with a porous boundary to provide a hydrodynamic flow of the sweep gas there will always be a passage oi sweep gas into the coke oven gas as well as the diflusion of some constituents of the sweep gas through the boundary into the coke oven gas. At the same time there will be a passage of constituents or the coke oven gas into the sweep gas, 16 particularly those constituents which have a low molecular weight (hydrogen and low boiling point hydrocarbons). The rate of diflusion or various gases through a porous boundary is roughly inversely proportional to the square root of the molecular weight of the gas passing through the porous openings. Therefore, those lower molecular weight gases have a higher velocity or rate of passage through the boundary than the heavy molecular weight constituents. In some cases the movement of sweep gas in one direction will entirely oppose the movement of heavy constituents from the coke oven gas in the opposite direction. By this means a. selective separation of the gases may take place. The greater the resistance to flow through the boundary or the smaller the porosity the more concentrated will be the hydrogen gas passing through the boundary. This same principle applies to all of the gases and the higher the molecular weight the less the difiusion of such gases through the boundary.

The porous boundary tubes 22 which are illustrated in the drawings are of a material which is known on the market as Lektromesh which is a copper screen coated with nickel to make it corrosion resistant. Many other types of boundaries may be used for this purpose, the effectiveness of the boundary depending upon the size and uniformity of the porous openings in the boundary through which the gases may difiuse.

In Tables II and III below are shown examples of the revision of coke oven gas with a mixture of producer gas and steam as a sweep gas when using seven Lektromesh tubes, 1% inches inside diameter and 24 inches in effective length. The Lektromesh barrier has 6400 openings per square inch, each opening being substantially square, the length of a side of the opening being 0.0035 inch. The flow rates of feed and sweep gases are corrected to 30 inches of mercury at a temperature of 60 F.

TABLE II Dz'fiusion pilot plant Producer gas steam countercurrent to coke oven gas fiow. Boundary: 80 x 80 x 0.0035" Lektromesh-7 tubes 1 in diameter x 24" Eiiective length- -547 .9 Flow rates at 30" Hg+60 F.:

Feed coke oven gas in=390 cu. it./hr. Feed coke oven gas out=517 cu. ft./hr.+24.4

lbs/hr. steam Sweep (prod. gas) in=482 cu. it./hr.+65.9

lbs/hr. steam Sweep (prod. gas) out=355 cu. ft./hr.+41.5

lbs/hr. steam Bwee Prod.

8 Feed In Out In Out Per- Per- Per- Percent cent cent cam 13,5 Conductivity Cell 11.6 26.0 54.3 37.7

lSfi Z 002 4.0 3.5 1.7 4.9 Unsats 0.0 0.0 2.6 1.7 01.. 0.2 0.1 0.7 0.7 H," 12.4 26.2 54.9 36.9 c 28.5 24.3 6.3 14.1 CH4. 1.4 0.2 24.0 17.3 0213. 1.2 2.3 0.6 1.1 511 by diiierence 51.4 43.4 8.6 23.3 Specific gravity 0.889 0.751 0.394 0.595

TABLE III Difiusion pilot plant Producer gas steam countercurrent to coke oven gas flow. Boundary: 80 x 80 x 0.0035" Lektromesh-I tubes 1%" in diameterx24" Efiective length-547.9 Flow rates at 30" Hg+60 F.:

Feed coke oven gas in=390 cu; ft./hr. Feed coke oven gas out=495 cu. ft.-/hr.+9.1

lbs/hr. steam Sweep (prod. gas) in=473 cu. tt./hr.+24.5

lbsJhr. steam l Sweep (prod. gas) out=368 cu. tt./hr.+l5.4

lbs./hr. steam Swee Prod.

as Feed In Out In Out Per- Per- Pcr- Peran! 061]! cent cent H; by Conductivity Cell. 11.6 29.8 54.3 37.3

Orsat:

co, 4.9 3.6 1.7 3.1 Unsats 0.0 0.2 2.6 20 0=. 0.2 112 0.7 0.5 1211.- 1a4 28.5 54.9 30.3 00. 28.5 2;.4 as 14.3 CH1. 1.4 0.0 240 1110 0 Cd-Ih 1.2 1.1 0.8 0.8

N; bydiiierence 51.4 42.4 8.5 13.6. Specific gravity 0.889 0.727 0.394 0.480

Similar runs have been made with the same coke oven gas and sweep gas wherein the flow through the diffusion apparatus is in concurrent paths as distinguished fromthe flow in countercurrent paths as shown in Tables II and 111. When the gas flows in concurrent paths the sweep gas flows from the line 40 through a valved line 86 into the chamber 48, then up through the tubes 00 into the chamber 44, then out through the lines 42 and 52 into the cooler 54. The passage from the cooler is then through the measuring 45 column 56, separator 58 and meter 62.

It will be understood that valves are placed in the lines 40, 32 and to direct the flow of sweep gases through the diffusion apparatus in either concurrent or countercurrent directions of 50 flow with reference to the direction of flow of the coke oven gas.

By this means a selective removal or separation of predetermined constituents in the various gas streams may be made to get practically any desired revision of the gas. The hydrogen passing most rapidly from the coke oven gas to the producer gas acts to increase the B. t. u. value of the producer gas and at the same time increases the B. t. u value of the coke oven gas.

Furthermore, this difiusion movement of constituents through the boundary permits an increase in the specific gravity in the coke oven gas and a slight lowering of the specific gravity of the producer gas.

A typical blast furnace gas has a specific gravity of about 9.0 and a B. t. 11. value of about 85. Carbon dioxide is 11.5%. hydrogen 1%, carbon monoxide 27.5%, and nitrogen 60%. It will be seen that with a blast furnace gas a comparatively 7 large amount of hydrogen may be transferred by difiusion to build up its B. t. u. value and change its specific gravity. On the other hand, a typical producer gas which contains 10% of hydrogen would not require the transfer of as much hydro- 7 gen by diffusion in order to increase its B. t. u.

'asoasse 7 value and change its specific gravity. The use of steam with these gases gives an excellent control for the modification oi the composition of the gases in that, when part oi the sweep gas fiowing throughthe boundary is a condensable vapor which is later removed from thejrevised coke oven gas, the addition of producerggga's or blast iurnace gasto the coke ovengas stream relative to the amount of hydrogen transferred to the sweep gas side by difiusion is reduced.

The preferred form of the invention having been thus described, what is claimed as new is:

1. A method of simultaneously changing the composition and specific gravity of coke oven gas and producer gas comprising: feeding coke oven gas as a stream along one side of a porous boundary, passing producer gas in mixture with steam to sweep across the other side of the boundary. controlling the area and length 01' the boundary and the rate oi how of gas on each side of the boundary to secure a difiusion of hydrogen from the coke oven side to the producer side of the boundary and to cause a flow of nitrogen, steam and carbon monoxide from the producer gas to the coke oven gas side of the boundary to increase the specific gravity of the coke oven gas from 37.5 to 75%, and removing steam from each of the gas streams.

2. The method of changing the composition of iuel gases defined in claim 1 in which the gas streams pass along the porous boundary in countercurrent paths.

3. The method of revising iuel gasa as defined in claim 1 in which the steam passing across the boundary is dry steam and in which the temperature of the gas streams at each side of the boundary is maintained above the dew point of steam.

4. The method of revising the composition of fuel gases defined in claim 1 in which the gases are circulated across the boundary in concurrent paths.

5. The method defined in claim 1 in which a slightly higher pressure is maintained on the sweep gas side of the boundary than on the coke oven gas side or the boundary to cause a hydrodynamic fiow of producer gas and steam through the pores of the boundary to the coke oven gas side of the boundary.

'6. The method defined in claim 1 in which the volume of producer gas passing across the boundary is at least 20% greater than the volume of 8 coke oven gas passing aerou the boundary and the volume 01 steam flowing with the producer gas is from 3% to 25% by volume or the volume of producer gas.

'1. The method defined in claim 1 in which the composition or the coke oven gas producer gases are brought to a finished composition in a single pass across the boundary.

8. A ,method 01' simultaneously changing the composition and specific gravity of coke oven gas and a fuel gas of high molecular weight comprising: ieeding coke oven gas as a stream along one side of a porous boundary. a high molecular weight gas in admixture with steam to sweep across the other side oi the boundary, controlling the area and length 01 the boundary and the rate oi flow oi the gases on each side oi the boundary to secure a difiusion oi hydrogen irom the coke oven gas to the high molecular weight iuei gas stream and to cause a fiow of nitrogen. carbon monoxide and steam from the high molecular weight gas side 01 the boundary to the coke oven gas side of the boundary to increase the specific gravity of the coke oven gas from 37.5 to and removing steam from each gas stream.

9. The method defined in claim 8 in which the volume of high molecular weight iuel gas is greater than the volume of coke oven gas.

10. The method defined in claim 8 in which the volume of high molecular weight gas is greater than the volume of coke oven gas and the volume of steam is from3% to 25% by volume of the high molecular weight gas.

11. The method defined in claim 8 in which the high molecular weight gas is blast i'urnace gas.

EARL V. HARLOW.

REFERENCES CITED The following references are of record in the file oi this patent:

UNITED STATES Pa'mm's 

